Micro-fluidic test apparatus and method

ABSTRACT

An apparatus, system, and method for determining the osmolarity of a fluid. The apparatus includes at least one micro-fluidic circuit and at least one electrical circuit disposed in communication with the micro-fluidic circuit for determining a property of a fluid contained within the at least one micro-fluidic circuit.

FIELD OF THE INVENTION

The invention generally relates to an apparatus, system, and method formeasuring the osmolarity of a relatively small volume of fluid, and moreparticularly to an apparatus, system, and method for measuring theosmolarity of human tears.

BACKGROUND

Dry eye syndrome (DES), also known as keratoconjunctivitis sicca (KCS),is a condition that occurs due to loss of water from the tear film andis one of the most common complaints seen by optometrists. Studies havefound that DES is common in about 15% of patients over the age of 50,with prevalence increasing with age. Dry eye in general is caused by anycondition that increases tear film evaporation or by any condition thatdecreases tear production. For example, evaporation may be increased asa result of having larger eyes (i.e., having more surface area forevaporation to occur from). Also, tear production may decrease from anycondition that decreases corneal sensation, such as long term contactlens wear, laser eye surgery, trauma to the 5^(th) nerve, and certainviral infections, etc.

The treatment of DES depends on the severity of the condition. Somepatients find relief through the use of various artificial tears. Othersutilize supplements containing Omega-3. Still others resort to theinsertion of punctual plugs to stop the drainage of tears. Effectivetreatment, however, begins with effective diagnosis.

In order to diagnose DES, it is useful to determine the osmolarity ofthe tears in the affected eye. Osmolarity is the measure of theconcentration of osmotically active species in a solution, and may bequantitatively expressed in osmoles of solute per liter of solution. Itis known that when the tear film loses water, salt and proteinconcentrations increase relative to the amount of water, resulting inincreased osmolarity. Therefore, in order to diagnose and treat DESpatients, it is desirable for a treating physician to quantify theosmolarity of a sample tear fluid.

Current techniques for measuring osmolarity involve osmotic pressuremeasurement, freezing point depression analysis, vapor pressuremeasurement, and electrical resistance measurement. In one approach, anosmometer is used to measure the osmotic pressure exerted by a solutionacross a semi-permeable membrane. The osmotic pressure can be correlatedto the osmolarity of the solution.

In another approach, the osmolarity of a sample fluid may be determinedby an ex vivo technique that involves analyzing the freezing point ofthe sample fluid. Deviation of the sample fluid freezing point from 0°Celsius is proportional to the solute level in the sample fluid, and isindicative of the osmolarity.

In a further known ex vivo technique, a piece of filter paper is placedunder the patient's eyelid to absorb tear fluid. The paper is removedand placed in an apparatus that measures a dew point. The reduction indew point proportional to that of water can be converted to anosmolarity value.

Lastly, osmolarity may be determined by measuring the conductivity of afluid sample. The measurement may be made in vivo by placing electrodesunder the eyelid. Alternatively, the measurement may be made ex vivo bycollecting a sample from the patient and transferring it to ameasurement apparatus.

Known techniques for measuring osmolarity, such as those describedabove, rarely produce accurate or consistent results because they sufferfrom problems including, for example, inducement of reflex tearing andevaporation of fluid samples. Reflex tearing occurs when the tear glandsof the patient are stimulated during tear collection. The stimulationproduces extra amounts of liquid, which can lead to false readings(e.g., too high water content). Conversely, when very small samples aretaken to avoid reflex tearing, the small samples often immediately beginto evaporate, which can lead to false readings (e.g., too low watercontent).

Accordingly, there exists a need in the art to overcome the deficienciesand limitations described hereinabove.

SUMMARY OF THE INVENTION

In a first aspect of the invention, an apparatus comprises at least onemicro-fluidic circuit and at least one electrical circuit disposed incommunication with the micro-fluidic circuit for determining a propertyof a fluid contained within the at least one micro-fluidic circuit.

In a second aspect of the invention, a system for measuring osmolarityof a fluid comprises a carrier comprising a through hole, a gripper, amover, and an expeller. The through hole is structured and arranged tobe aligned with a test site. The gripper is structured and arranged togrip a collector. The mover is structured and arranged to align thecollector with the through hole.

In a third aspect of the invention, a method for determining osmolarityof a fluid comprises receiving into a gripper a collector having a fluidsample and moving the collector into alignment with a test site. Themethod further comprises expelling the fluid sample from the collectorinto the test site, measuring a property of the fluid sample within thetest site, and displaying a value of the property.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows top view of a test chip according to aspects of theinvention;

FIG. 2 shows sectional view taken along line 2-2 of FIG. 1;

FIG. 3 shows sectional view taken along line 3-3 of FIG. 1;

FIG. 4 shows bottom view of the test chip according to aspects of theinvention;

FIG. 5 shows a schematic representation of a circuit according toaspects of the invention;

FIG. 6 shows a schematic representation of a determiner according toaspects of the invention;

FIG. 7 shows a system according to aspects of the invention;

FIG. 8 shows a combined gripper and expeller according to aspects of theinvention;

FIG. 9 shows a system according to aspects of the invention;

FIGS. 10A and 10B show another system according to aspects of theinvention; and

FIGS. 11-14 show flow diagrams depicting methods according to aspects ofthe invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is directed to a system and method for determining theosmolarity of fluids, such as, for example, human tears. According tothe invention, the osmolarity of a fluid can be determined in aclinically feasible manner, on a nanoliter scale, and with thecapability for reduced evaporation, by measuring at least one electricalproperty (e.g., resistance, conductivity, etc.) of the fluid. In thismanner, implementations of the invention may be used for providingaccurate and consistent osmolarity measurements, thereby facilitatingthe diagnosis and treatment of pathological conditions.

FIG. 1 shows a chip 10, according to implementations of the invention.The chip 10 is provided with at least one test site that can be used fordetermining at least one electrical property (e.g., resistance,conductivity) of a fluid. The osmolarity of the fluid may be determinedfrom a predetermined correlation to the determined electrical property.

In embodiments, chip 10 has a first side edge 12, second side edge 14,and first surface 15 on which is located at least one test site 20.Although the chip 10 is shown as rectangular, it is understood that thechip 10 may have any shape (e.g., oval, circular, etc.) In embodiments,the chip 10 has eighteen test sites 20, although other numbers of testsites are contemplated by the invention. The test site(s) 20 may bearranged in any suitable pattern (e.g., rectangular grid, radially,etc.) on the chip 10. Each test site comprises a first hole (e.g., largehole 25) and a vent hole 35. Moreover, each test site 20 furthercomprises a second hole comprising a first portion (e.g., small hole 30)having a diameter smaller than the first hole, and a connecting tunnel(shown as 40). The large hole 25, small hole 30, tunnel 40, and venthole 35 combine to form a micro-fluidic circuit, described in greaterdetail below. Although the invention is described in terms of amicro-fluidic circuit, it is understood that the invention may beimplemented in any suitable scale (e.g., micro-fluidic, nano-fluidic,etc.). In embodiments, individual or multiple chips 10 may be packagedin a protective vacuum-sealed bag.

The chip 10 may be composed of any suitable material. In embodiments,the chip 10 is composed of a layered structure (for example, a ceramiclaminate structure formed by stacking and sintering multiplepersonalized layers). For example, as shown in FIG. 2, the chip 10 maycomprise six layers (L1, L2, L3, L4, L5, L6) of glass ceramic material,each layer being composed of a mixture of silica, alumina, magnesia, andbinder (e.g., organic binder). Each layer may have a thickness of about2 mils to 6 mils.

In embodiments, each layer and its associated features are separatelyformed and then assembled to create the chip 10. For example, a holehaving a diameter of about 1100 microns is formed in the first layer L1to create the large hole 25. The large hole 25 may be formed in anysuitable manner, such as, for example, cutting, laser drilling, waterknife, sand blasting, overlap punching, etc. Similarly, a hole having adiameter of about 300 microns is formed in the first layer L1 to createthe vent hole 35. A hole having a diameter of about 500 microns isformed in the second layer L2 to create the small hole 30. And a holeconnected to and extending from the small hole 30 and having a width ofabout 100 microns and a length of about 3500 microns is formed in thesecond layer L2 to create the tunnel 40. It is noted that other suitabledimensions may be employed. The layers are stacked such that the largehole 25 overlaps the small hole 30, and the vent hole 35 overlaps an endof the tunnel 40. In this way, an enclosed (e.g., buried) micro-fluidiccircuit is formed that is less susceptible to the effects ofevaporation.

When a fluid sample (e.g., a tear) is deposited in the large hole 25,the fluid will flow into the offset small hole 30 by way of gravity. Thefluid will flow from the small hole 30 into the tunnel 40, toward thevent hole 35, by capillary action. The rate at which the fluid flowsthrough the tunnel 40 can be estimated from the rate of capillary action(e.g., from the dimensions of the micro-fluidic circuit and theproperties of the fluid) and the rate of evaporation of the fluid. Thetime from depositing the fluid into the large hole 25 to the fluidreaching any location in the tunnel 40 may be estimated with the rateand known dimensions of the micro-fluidic circuit.

In addition to the micro-fluidic circuit, each test site 20 includes atleast one electrical circuit for measuring at least one electricalproperty (e.g., resistance) of the fluid contained in the micro-fluidiccircuit. In embodiments, the electrical circuit comprises lines ofelectrically conductive material deposited in holes formed throughlayers L3, L4, L5, and L6, as shown in FIG. 3. For example, vias 45 areformed in substantially identical locations in layers L3, L4, and L5.Larger pads 50 are formed in corresponding holes in bottom layer L6.

The pads 50 are exposed on the bottom surface 52 of the chip 10, asshown in FIG. 4, such that measuring equipment may be electricallyconnected thereto. Each via 45 and pad 50 may comprise, for example, ahole formed in the respective layer and filled with an electricallyconductive material. The electrically conductive material may be anysuitable material, such as, for example, gold, silver, copper, nickel,platinum, etc., and composites thereof. In embodiments, the electricallyconductive material comprises a metal paste that is composed of amixture having about 56% copper, 14% nickel, and 30% glass (e.g., glassceramic) by volume. This composition is resistant to oxidation instorage and use, and has a very low resistance relative to that ofintended sample fluids.

In the exemplary implementation shown in FIG. 5, six different vias 56,58, 60, 62, 64, and 66 are shown as part of the electrical circuit for atest site 20. Two vias 56 and 58 are disposed within the perimeter ofthe small hole 30. Two vias 60 and 62 are formed on either side of thetunnel 40 at a first downstream location along the tunnel 40. Two vias64 and 66 are formed on either side of the tunnel 40 at a seconddownstream location along the tunnel 40. Additionally, a first electrode68 extends across the tunnel 40 connecting vias 60 and 62, and a secondelectrode 70 extends across the tunnel 40 connecting vias 64 and 66. Inembodiments, the first and second electrodes are formed by depositing anelectrically conductive material on the surface of third layer L3. Forexample, the same metal paste as used in the vias may be printed ontothe third layer using known techniques.

Still referring to FIG. 5, the two electrodes 68, 70 traverse the tunnel40 at locations downstream from the small hole 30. The respective viasare electrically connected as schematically shown by dotted lines. Whena fluid fills the small hole 30, the fluid will create an electricalconnection between the vias 56 and 58. The resistance of the fluidbetween the circuit elements A1:B1 may be measured in a known manner, asdescribed in greater detail below. Moreover, the time of the measurementmay be noted, such as, for example, by starting a timer. As the fluidmoves through the tunnel 40 by capillary action, it will cross firstelectrode 68. At this point, the resistance of the fluid between thecircuit elements B2:B1 may be measured. As the fluid continues to movethrough the tunnel 40, it will cross second electrode 70, at which pointthe resistance between circuit elements A2:A1 may be measured.Similarly, a measurement may be made between the first electrode 68 andsecond electrode 70.

In embodiments, the above-described features may be varied to achievedesired effects on the fluid sample. For example, the diameter of thevent hole and the diameter of the cross-section of the tunnel may bekept small to reduce the area of the air-liquid interface so as toreduce evaporation of liquid from the fluid sample. Furthermore, theseparation distances between the small hole and the first electrode, orbetween the venting hole and the second electrode can be made large toincrease the time needed for diffusion of species toward the electrodes.Even further, the tunnel may be formed in a non-linear path (e.g.,curved, zigzag, meandering, etc.) to increase the distances fordiffusion without making the footprint of the micro-fluidic circuitsubstantially larger.

FIG. 6 schematically shows a determiner 80 for determining theosmolarity of a fluid sample held in the micro-fluidic circuit of a testsite. In embodiments, electrically conductive probes 82 a, 82 b areconnected to two respective pads (50′ and 50″) of a chip. For example, afirst probe 82 a (e.g., pogo probe, alligator clip, etc.) may be laidupon, clipped to, or slidingly brought into contact with a first padthat is connected to a first via 60, and a second probe 82 b maysimilarly be brought into contact with an other pad that is connected toan other via 64. In embodiments, the probes 82 a, 82 b are alsoconnected to a measuring device 84, bridge 85, and current generator 86.For example, the measuring device 84 may comprise an rms voltmeter, thebridge 85 may comprise a 100 Kohm resistor, and the current generator 86may comprise a signal generator. When a fluid sample is placed in thelarge hole 25 and fills the small hole 30, the fluid will close acircuit between vias 60, 64. A current, such as, for example, a 100 kHzsinusoidal signal from the generator 86, can be applied to the circuit,and at least one electrical property (e.g., resistance) of the fluid maybe determined, as will be understood by those of skill in the art.Certain electrical properties (e.g., conductivity, resistance) of thefluid are directly related to the ion concentration of the fluid in aknown manner. Because the ion concentration is related to the osmolarityof the fluid, the osmolarity may be determined from the at least onemeasured electrical property.

Similar measurements can be made when the fluid closes the circuitbetween first electrode 68 and via 58, and when the fluid closes thecircuit between second electrode 70 and via 56. Although two electrodesare depicted, any number of electrodes may be used at any locationsthroughout the micro-fluidic circuit. In this manner, numerousmeasurements of the same property of the fluid may be made and compared,thereby increasing the reliability that the measurements are accurate.For example, a routine statistical analysis may be performed on thenumerous measurements to determine a confidence factor that can then becompared to a pre-determined pass/fail threshold.

In embodiments, the determiner 80 comprises a display 90 that displaysthe measured value from the measuring device 84. For example, thedisplay 90 may comprise an LCD display that displays a numerical valuethat corresponds to the measured electrical property of the fluid. Auser may utilize a reference chart, based upon known correlation betweenthe measured electrical property and the osmolarity, to convert thedisplayed numerical value to an osmolarity value. Optionally, acorrelating device 95 that automatically correlates the measuredelectrical property to the osmolarity may be disposed between themeasuring device 84 and the display 90. The correlating device 95 maycomprise, for example, a computer processor that receives the value ofthe measured electrical property, converts the value of the measuredelectrical property to an osmolarity value by accessing look-up tablesor correlation equations, and outputs the osmolarity value to thedisplay 90.

FIG. 7 shows a system 100 according to aspects of the invention. Inembodiments, the system 100 comprises a collector 102, carrier 105, andtest stand 110. The system 100 may also include a chip 10 as describedabove. In this manner, the system may be used to determine theosmolarity of a fluid.

In embodiments, the collector 102 comprises a micropipette or acapillary tube, and is used for collecting the fluid sample to betested. For example, a micropipette can be used to collect a tear fromthe human eye by way of capillary action and without inducing reflextearing, as is known in the art. In embodiments, the collector 102 issized to correspond to other elements of the system, as described below.For example, an outside diameter of an end of the collector 102 may besized smaller than a diameter of the large hole but larger than adiameter of the small hole of a test site.

The carrier 105 includes a holding structure 120 for holding andaligning a chip. The holding structure 120 may be shaped and sized inany suitable manner, and may be composed of any suitable material. Inembodiments, the holding structure 120 comprises a plate-like memberthat is formed of plastic, such as, for example, by injection molding.The holding structure 120 includes a receiving portion 125 that receivesthe chip. In implementations, the receiving portion 125 may be a slotdisposed within the holding structure 120, and the chip may be slidinglyreceived into the slot.

The holding structure 120 also includes funnels 130 that are arranged tobe disposed above the respective test sites of a chip that is held inthe receiving portion 125. For example, there may be eighteen funnels130 that align with portions (e.g., the large holes) of the eighteentest sites of a chip that is held in the receiving portion 125. Thefunnels 130 facilitate precise placement of fluid samples onto therespective test sites (e.g., into the large holes).

In embodiments, the carrier 105 further comprises alignment devices,such as, for example, pegs 140 disposed on the top surface of theholding structure 120. The pegs 140 may be integral with or separablefrom the holding structure 120. The pegs 140 facilitate alignment of thecarrier 105, and therefore the test sites of a chip held therein, withthe test stand 110.

Still referring to FIG. 7, the test stand 110 includes a housing 145, amover 150 adapted to move the collector 102, an expeller 155 adapted toexpel a fluid sample from the collector 102, and a gripper 160 adaptedto grip the collector 102.

The housing 145 is adapted to be removably connected to the carrier 105via the pegs 140. In this manner, the test sites located on the chipwithin the carrier 105 may be precisely aligned with the other elementsof the housing 145. The housing 145 may be of any suitable size andshape, and may be constructed of any suitable material.

The mover 150 is adapted to align a gripped collector 102 with arespective funnel 130 of the carrier 105. In embodiments, the mover 150comprises any combination of one or more actuators (e.g., screw, rackand pinion, pneumatic, etc) that is arranged to move the collector 102back and forth along three orthogonal axes (e.g., x, y, and z, as shownin FIG. 7). The mover 150 may also comprise one or more controllers(such as, for example, a programmable logic controller, microprocessor,etc.) for controlling the actuator(s). Such actuators and controllersare known in the art and may be housed separately from or within thehousing 145. With knowledge of the dimensions of the housing 145,carrier 105, and collector 102, the mover 150 may be used to move thecollector 102 into precise alignment with a respective funnel 130. Oncealigned with a funnel 130, the mover 150 may cause the collector 102 tomove through the funnel 130 to a position aligned with, and just above,a respective test site. In this manner, a fluid sample may be preciselyaligned with a test site before the fluid sample is expelled from thecollector 102 onto the chip.

The expeller 155 is adapted to expel the fluid sample from the collector102 and onto the chip. In embodiments, this is accomplished byincreasing the air pressure behind the fluid sample held in thecollector 102. This may be accomplished in any known manner, such as,for example, using an elastic bulb, air pump, air compressor, etc. Theincreased air pressure pushes the sample out of the collector 102. Whenthe collector 102 is aligned with the test site, as described above, thesample is expelled onto the test site (e.g., into the micro-fluidiccircuit). The expeller, or components thereof, may be located inside oroutside the housing 145.

The gripper 160 is adapted to receive and hold the collector 102 suchthat the collector may be appropriately moved and the fluid sampleexpelled, as described above. In embodiments, the expeller 155 andgripper 160 are combined, as shown in FIG. 8. In this implementation,the gripper 160 comprises a gripper body 165 that hinges open and closedabout an axis that is offset from and parallel to the longitudinal axisof the collector 102. When the gripper body 165 is hinged open, thecollector 102 may be received in a seal portion 170. When the gripperbody 165 is hinged closed around the collector 102 (as shown in FIG. 8),the seal portion 170 is arranged to grip the collector 102 withoutdamaging it, and to provide a substantially airtight seal around thecollector 102. Moreover, when the gripper body 165 is closed around thecollector 102, the top end of the collector 102 is disposed within a gap175.

Still referring to the implementation shown in FIG. 8, the expeller 155comprises an elastically deformable membrane 180 that forms part of theboundary of the gap. In embodiments, the membrane 180 is composed of anelastomeric material, although any suitable material may be used. Theexpeller 155 also comprises any suitable device (e.g., piezoelectricactuator, air pump, etc.) for applying a force to the membrane 180 thatwill move the membrane 180 into the gap (as shown by the arrow in FIG.8). Movement of the membrane 180 into the gap increases the pressurebehind the fluid sample in the collector 102, such that the fluid samplewill be expelled from the collector 102.

Further aspects of the system 100 are shown in FIG. 9. In embodiments,the holding structure 120 may comprise electrical contact portions 185that are structured and arranged to come into contact with respectivepads of a chip that is disposed in the receiving portion 125 of thecarrier 105. The electrical contact portions 185 may be connected to ameasuring device, as will be apparent to the skilled artisan, such thatthe osmolarity of the fluid in a particular test site may be determined.For example, for a chip having eighteen test sites and six pads per testsite, the holding structure 120 may be provided with one hundred andeight (i.e., six times eighteen) individual contact portions 185. Inthis manner, every single pad of the chip will be in contact with arespective contact portion 185 of the carrier when the chip is receivedin the receiving structure 125.

In embodiments, the contact portions 185 are further connected to adeterminer 80, such as that described above, for determining theosmolarity of the fluid(s) in the test site(s). For example, the contactportions 185 may be connected (e.g., wired) to a selecting device 190(e.g., switch, processor, microprocessor, etc.) that is, in turn,connected to the probes of the determiner 80. As will be understood bythe skilled artisan, the selecting device 190 can be operated to isolateany two respective contact portions 185, such that the resistance of thefluid that completes the circuit between the pads that are in contactwith the two respective contact portions 185 can be determined with thedeterminer 80. In this manner, the osmolarity of the fluid thatcompletes the circuit between the pads can be determined.

The selecting device 190 and/or determiner 80 may be housed separatelyfrom the other elements of the system 100, such as, for example, in ahandheld device or desktop computer. Alternatively, the selecting device190 and/or determiner 80 may be integrated into the carrier 105 or teststand 110. Additionally, an input device (e.g., keypad, buttons,switches, etc.) for providing input to the various controllers of thesystem may be housed separate from or integrated with the carrier 105 ortest stand 110.

FIGS. 10A and 10B show an alternative system 200 according to aspects ofthe invention. In this embodiment, the system comprises a collector 202,carrier 205, and test stand 210. The collector 202 and carrier 205 maybe similar to those described above. In embodiments, the test stand 210includes a housing 245, mover 250, expeller 255, and gripper 260, whichmay be similar to those described above.

In this implementation, the test stand 210 also comprises a hinged door300 attached to the housing 245, as shown in FIG. 10B. The hinged door300 may carry portions of the carrier 205, mover 250, expeller 255, andgripper 260. The door 300 may be opened for insertion of a chip, carrier205, and collector 202 (with fluid sample) into the test stand 210. Whenthe door 300 is closed, the system 200, via actuators and controllers,moves the collector 202 to the appropriate funnel of the carrier 205 andexpels the fluid sample onto a test site. The movement and expelling maybe automatic upon closing the door 300, or may require user input (e.g.,from buttons, keypad, switch, etc.).

The system 200 (as well as the system 100 described above) may includean output display 320 (e.g., LCD, computer screen, etc.) for displayinginformation, such as, for example, the values determined by thedeterminer, menus and/or instructions for a user, etc. Additionally, thesystem 200 (as well as the system 100) may include an input device 325(e.g., buttons, keypad, switch, etc.) for receiving input from a user.The display 320, input device 325, and a determiner (as described above)may be integrated into the housing 245.

Method of Use

FIGS. 11-14 are flow diagrams implementing steps of the invention. FIGS.11-14 may equally represent a high-level block diagram of the invention.Some of the steps of FIGS. 11-14 may be implemented and executed fromeither a server, in a client server relationship, or they may run on auser workstation with operative information conveyed to the userworkstation to create the navigation outlined above. Additionally,aspects of the invention can take the form of an entirely hardwareembodiment, an entirely software embodiment or an embodiment containingboth hardware and software elements.

In an embodiment, aspects of the invention are implemented in software,which includes but is not limited to firmware, resident software,microcode, etc. Furthermore, aspects of the invention can take the formof a computer program product accessible from a computer-usable orcomputer-readable medium providing program code for use by or inconnection with a computer or any instruction execution system. For thepurposes of this description, a computer-usable or computer readablemedium can be any apparatus that can contain, store, communicate,propagate, or transport the program for use by or in connection with theinstruction execution system, apparatus, or device. The medium can be anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system (or apparatus or device) or a propagation medium.Examples of a computer-readable medium include a semiconductor or solidstate memory, magnetic tape, a removable computer diskette, a randomaccess memory (RAM), a read-only memory (ROM), a rigid magnetic disk andan optical disk. Current examples of optical disks include compactdisk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) andDVD.

FIG. 11 shows a first method 400 according to a first aspect of theinvention. At step 405, a sample of fluid is collected for the purposeof determining the osmolarity of the fluid. In embodiments, the sampleis collected with a collector, such as, for example, a micropipette orcapillary tube, as described above. Such a collector may be used to drawfluid (e.g., tear, blood, etc.) from a patient (e.g., human, dog, cat,etc.), as should be apparent to those skilled in the art.

At step 410, the sample is deposited onto a test site. In embodiments,this comprises using one of the previously described systems 100, 200 todeposit the sample onto a test site of a chip such that the sampleenters the micro-fluidic circuit. For example, a collector may bealigned with a portion of a test site (e.g., the large hole of the testsite), and the sample expelled from the collector by increasing the airpressure behind the sample such that the sample is expelled onto thetest site.

At step 415, at least one electrical property of the fluid is measured.In embodiments, this is accomplished using the determiner describedabove as the sample moves through the micro-fluidic circuit by capillaryaction. For example, a current may be applied to the appropriateelectrical circuit, and the resistance (or conductance) of the fluid maybe measured in a known manner.

At step 420, the measured value of the at least one electrical propertyof the fluid is correlated to an osmolarity value of the fluid. Inembodiments, this is accomplished using a microprocessor that applies alook-up table or correlation equation to the value of the measuredelectrical property. Then, at step 425, the osmolarity value isdisplayed. In embodiments, the value is displayed on an LCD, computerscreen, or similar display.

FIG. 12 shows a second method 430 according to a second aspect of theinvention. The steps 405′, 410′, and 415′ may be performed in a mannersimilar to steps 405, 410, and 415 of first method 400. However, in thesecond method 430, the value of the measured property is displayed atstep 435 before correlating it to the osmolarity at step 440. Forexample, the value of the measured property, such as, for example, avoltage that corresponds to the measured property, is displayed at step435. Then, at step 440, a user manually correlates the value to anosmolarity value by, for example, referring to a written chart. In thisway, the second method 430 may be implemented without using an automaticcorrelating device (e.g., microprocessor).

FIG. 13 shows further exemplary details of step 410 according to aspectsof the invention. It is understood that FIG. 13 may also representexemplary details of step 410′. Moreover, while FIG. 13 is describedbelow with respect to the first system 100, it is understood thatsimilar steps may be performed in association with the second system 200(or any other system within the scope of the invention).

At step 500, after a fluid sample has been collected, a chip isconnected to a carrier and both are connected to a test stand. Inembodiments, this comprises inserting a chip into receiving portion ofcarrier such that the pads of the chip contact the contact portions. Thecarrier is then connected to the test stand via the pegs. Alternatively,the carrier may first be connected to the test stand, and then the chipconnected to the carrier. In this manner, the various electricalcircuits of the chip are brought into communication with the selectingdevice and determiner via the pads and contact portions. Moreover, as aresult of step 500, the test sites of the chip are spatially located inknown positions relative to the test stand such that a collector may beprecisely aligned with a test site.

At step 510, the collector is inserted into the gripper. In embodiments,the combination gripper/expeller shown in FIG. 8 is used. For example,step 510 may comprise opening the gripper body, placing the collectoralong the seal portion such that the top of the collector extends intothe gap, and closing the gripper body around collector. In this manner,the collector (and, therefore, the fluid sample held therein) isconnected to the test stand such that it may be moved to and preciselyaligned with a test site.

At step 515, the gripper is moved to align the collector with arespective test site. In embodiments, this comprises using the mover tomove the gripper along any of three orthogonal axes. Because the testsites of the chip are spatially located in known positions relative tothe test stand, the mover may be pre-programmed to automatically movethe gripper such that the gripped collector is aligned with a particulartest site. After alignment of the collector above a test site, the movermay further move the gripper (e.g., axially in the direction of thelongitudinal axis of the collector) such that the a lower end of thecollector moves through a funnel and into a position just above thelarge hole of the particular test site.

At step 520, the fluid sample is expelled from the collector into themicro-fluidic circuit. For example, a force (as depicted by the arrowshown in phantom lines in FIG. 8) may be applied to the membrane of theexpeller. The movement of the membrane into the gap increases the airpressure behind the fluid sample in the collector, and pushes the fluidsample out of the end of the collector. As described above, the forcemay be applied to the membrane in any known manner (such as, forexample, by piezoelectric actuator, air pump, compressed air, etc.) andthe mechanism for applying the force may be integrated into the teststand.

Still referring to step 520, the fluid sample fills the large hole ofthe respective test site when it is expelled from the collector. Thefluid flows from the large hole into the offset small hole by way ofgravity and/or capillary action. The fluid continues to flow through thetunnel by way of capillary action, while the vent hole allows air thatwas in the tunnel to escape as the fluid fills the tunnel. At least oneproperty of the fluid may be measured while the fluid is flowing throughthe micro-fluidic circuit. By keeping the fluid at least partially (and,preferably, mostly) enclosed in the tunnel, the detrimental effects ofevaporation on such measurements may be minimized or avoided.

FIG. 14 shows further exemplary details of step 415 according to aspectsof the invention. It is understood that FIG. 14 may also representexemplary details of step 415′. Moreover, while FIG. 14 is describedbelow with respect to the first system 100, it is understood thatsimilar steps may be performed in association with the second system 200(or any other system within the scope of the invention).

At step 600, after a fluid sample has been deposited in themicro-fluidic circuit, the first of at least one electric circuit isactivated. For example, when the fluid fills the small hole, the fluidcreates a first circuit A1:B1 by providing an electrically conductiveconnection between vias 56 and 58 (see FIG. 5). In embodiments, theselecting device is used to activate this first circuit A1:B1 bybringing the respective pads of the vias 56, 58 into electricalcommunication with the probes 82 a, 82 b of the determiner. For example,the pad associated with via 56 is brought into communication with probe82 a, and the pad associated with via 58 is brought into communicationwith probe 82 b.

At step 605, a first of at least one property measurement of the fluidis taken. In embodiments, the determiner is used to measure theresistance of the fluid in the first circuit (e.g., between the vias 56,58) as described above. This first property measurement may be displayedand/or stored (such as, for example, in computer memory).

In embodiments, at step 610, a timer is started when the first propertymeasurement is taken (e.g. at step 605). For example, a timer (e.g.,counter) mechanism in a microprocessor may be started, as will beunderstood by the skilled artisan. The timer provides a mechanism forcoordinating multiple property measurements of the same fluid sample inthe same micro-fluidic circuit. That is, by knowing the rate ofcapillary action of the fluid through the micro-fluidic circuit, thetime at which the fluid reaches any point along the length of the tunnelmay be pre-determined. As such, by starting the timer when the fluidcloses the first electrical circuit, the timer may be used to dictatewhen to activate subsequent circuits along the length of the tunnel. Inthis manner, multiple property measurements may be taken atpredetermined locations and times.

At step 615, the first circuit is de-activated. This may comprise, forexample, using the selecting device to deactivate the circuit A1:B1 bytaking the vias 56, 58 out of communication with the determiner. Thefirst circuit may be de-activated at any time after the first propertymeasurement is taken but before activating the second circuit.

At step 620, the second circuit is activated. As the fluid flows throughthe tunnel (e.g., in the direction of the small hole toward the venthole), it will cross first electrode 68. At this point, the fluidcreates a second circuit B2:B1 by providing an electrically conductiveconnection between the first electrode 68 and the via 58 (see FIG. 5).In embodiments, the selecting device is used to activate this secondcircuit B2:B1 by bringing the respective pads of the vias 58 and 60 (or62) into electrical communication with the probes 82 a, 82 b of thedeterminer. For example, the pad associated with via 58 is brought intocommunication with probe 82 a, and the pad associated with via 60 isbrought into communication with probe 82 b.

At step 625, a second property measurement of the fluid is taken. Inembodiments, the determiner is used to measure the resistance of thefluid in the second circuit (e.g., between the vias 58, 60) as describedabove. This second property measurement may be displayed and/or stored(such as, for example, in computer memory). In embodiments, the secondproperty measurement is automatically taken at a predetermined timeinterval after the first measurement. This may be accomplished, forexample, based upon the timer value.

At step 630, the second circuit is de-activated. This may comprise, forexample, using the selecting device to deactivate the circuit B2:B1 bytaking the vias 58, 60 out of communication with the determiner. Thesecond circuit may be de-activated at any time after the second propertymeasurement is taken but before activating the third circuit.

At step 635, the third circuit is activated. As the fluid continues toflow through the tunnel, it will cross second electrode 70. At thispoint, the fluid creates a third circuit A2:A1 by providing anelectrically conductive connection between the second electrode 70 andthe via 56 (see FIG. 5). In embodiments, the selecting device is used toactivate this second circuit A2:A1 by bringing the respective pads ofthe vias 56 and 64 (or 66) into electrical communication with the probes82 a, 82 b of the determiner. For example, the pad associated with via56 is brought into communication with probe 82 a, and the pad associatedwith via 64 is brought into communication with probe 82 b.

At step 640, a third property measurement of the fluid is taken. Inembodiments, the determiner is used to measure the resistance of thefluid in the third circuit (e.g., between the vias 58, 60) as describedabove. This third property measurement may be displayed and/or stored(such as, for example, in computer memory).

In embodiments, steps 615-640 may be performed at respectivepredetermined time intervals after the first measurement is taken instep 605. The respective predetermined time intervals may be determinedbased upon the rate of capillary action of the fluid through themicro-fluidic circuit. The timer, started in step 610, may be monitoredto recognize when a particular predetermined time interval has elapsed.In this manner, the taking of multiple property measurements may beperformed automatically by a controller (e.g., processor) that monitorsthe timer and controls the determiner and selecting device.

Although steps 600-640 have been described with respect to threemeasurements and circuits, the invention may comprise any suitablenumber of circuits (and, therefore, measurements). Moreover, theelectrical circuits (e.g., vias and electrodes) may be disposed at anysuitable location along the micro-fluidic circuit.

If multiple measurements are taken, then a statistical analysis of themeasured values may be performed at step 645. In embodiments, a meanvalue and a confidence factor are calculated for all of the gatheredmeasurements. If the confidence factor exceeds a predetermined threshold(e.g., 90%), then the mean value is treated as valid. The mean value maybe correlated to an osmolarity value and then displayed (as in steps 420and 425) or, alternatively, displayed and then correlated to osmolarity(as in steps 435 and 440). An indication that the value is valid and/orthe confidence factor may also be displayed.

In embodiments, if the confidence factor does not exceed thepredetermined threshold, then the mean value is treated as invalid. Anindication that the value is invalid and/or the confidence factor may bedisplayed. Moreover, in addition to being displayed, any of the data(e.g., gathered measurements, mean value, confidence factor, osmolarity,etc.) may be stored (e.g., in computer memory, etc.) for later useand/or may be communicated over a network (e.g., LAN, WAN, Internet,wireless network, etc.).

While the invention has been described with respect to measuring theosmolarity of human tears, the invention is not limited to suchapplications. The invention can be used with other fluids, such as, forexample, blood, urine, sweat, plasma, semen, etc. Moreover, theinvention may be used to test the osmolarity fluids from any source(e.g., drinking water), not just those of humans. Thus, while theinvention has been described in terms of embodiments, those skilled inthe art will recognize that the invention can be practiced withmodifications and in the spirit and scope of the appended claims.

What is claimed:
 1. A system for measuring osmolarity of a fluid,comprising: a carrier comprising a through hole; a gripper; a mover; andan expeller, wherein the through hole is structured and arranged to bealigned with a test site, the gripper is structured and arranged to gripa collector, and the mover is structured and arranged to align thecollector with the through hole.
 2. The system of claim 1, wherein thecarrier further comprises a receiving portion arranged to receive a chipthat includes the test site.
 3. The system of claim 1, wherein the movercomprises at least one actuator and at least one controller arranged toautomatically align the collector with the through hole.
 4. The systemof claim 1, wherein the expeller comprises a device that expels a fluidsample from the collector by increasing air pressure behind the fluidsample in the collector.
 5. The system of claim 1, further comprising: afirst electrical contact portion structured and arranged to connect to afirst portion of an electrical circuit of the test site; a secondelectrical contact portion structured and arranged to connect to asecond portion of the electrical circuit of the test site; a deviceconnected to the first electrical contact portion and the secondelectrical contact portion, and structured and arranged to determine avalue of a property of a fluid contained within the test site; and adisplay connected to the device.
 6. The system of claim 5, furthercomprising a correlating device that receives the value of the propertyand generates an osmolarity value of the fluid, wherein the displaydisplays the osmolarity value.
 7. The system of claim 1, furthercomprising a device structured and arranged to: take plural measurementsof a property of a fluid disposed within the test site, calculate aconfidence factor of the plural measurements, and compare the confidencefactor to a threshold.
 8. The system of claim 1, wherein the carriercomprises: a receiving portion arranged to receive a chip that includesa plurality of test sites including the test site; and funnels that areabove respective ones of the plurality of test sites when the chip isheld in the receiving portion.
 9. The system of claim 1, furthercomprising a test stand wherein: a housing, the gripper, the mover, andthe expeller are included in the test stand; the housing is adapted tobe removably connected to the carrier via alignment devices; and themover is adapted to align the collector, gripped by the gripper, with afunnel of the carrier.
 10. The system of claim 9, wherein the expelleris adapted to expel a fluid sample from the collector, gripped by thegripper, onto the test site which is on a chip held in the carrier. 11.The system of claim 9, wherein the gripper comprises a gripper body thathinges open and closed about an axis that is offset from and parallel toa longitudinal axis of the collector.
 12. The system of claim 11,wherein the gripper and the expeller are combined.
 13. A method fordetermining osmolarity of a fluid, comprising: receiving into a grippera collector having a fluid sample; moving the collector into alignmentwith a test site; expelling the fluid sample from the collector into thetest site; measuring a property of the fluid sample within the testsite; and displaying a value of the property.
 14. The method of claim13, wherein: the moving comprises actuating an actuator that moves thegripper, the expelling comprises increasing air pressure behind thefluid sample disposed within the collector, and the measuring comprises:measuring plural values of the property; calculating a confidence factorfor the plural values; and comparing the confidence factor to athreshold.